Find/ascertain latest wordpress db from multiple database copies

It depends, but you may have the Generation Time of the file in the SQL file header, like this:

-- phpMyAdmin SQL Dump
-- version 4.2.10
-- http://www.phpmyadmin.net
--
-- Host: localhost:3306
-- Generation Time: Aug 08, 2016 at 10:50 AM
-- Server version: 5.5.38
-- PHP Version: 5.6.1